akamerica

From my D850 I import RAW (lossless compressed NEF) pictures to my computer. Post process some or all in Camera Raw, saving those modified as NEF. Then I choose to batch save all pictures as JPG 12 - max quality.

How - if at all - are the pictures that were NOT subject to modifications changed by being converted to JPG? If so, based on what settings?
How - if at all - are the post-processed pictures changed by being converted to JPG?

Inquiring minds want to know...

Art

PS. The processing that takes place in the camera to create a NEF or other adjustments when opening Camera Raw is not of concern.

Delderby Loc: Derby UK

Most photo editors will automatically apply SOME amount of adjustment when loading the RAW as a viewable file. This may be all the PP that is needed.

Longshadow Loc: Audubon, PA, United States

Look at the dates/time file stamp. Maybe the unmodified files were not "re-saved"?

Robertl594 Loc: Bloomfield Hills, Michigan and Nantucket

JPEGs use a compression that uses the data from the top left pixel of an 8x8 grid. It uses the full data from the one pixel and retains data that shows the difference, not the full data. Every time you open the file, work with it and resave it, it recalculated the difference, not saving the actual pixel data from the other 63 pixels. It’s fine to view, you should not experience any degradation if you don’t resave. If you plan on working on the image, use a lossless file format like TIFF.

kakima

The conversion applies the Picture Control and other settings in effect at the time of shooting, if they weren't changed in the editing.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

You aren't editing raw files and saving as nef. They enter your computer and remain untouched, even after editing.

Changes are either saved in a preview database if you are using catalog based applications like Lightroom, or in individual corresponding side car files - xmp if using Adobe products, dop if using DXO, etc.

When importing raw files some minimal processing takes place in order for you to be able to see them and edit them. You don't have much control over this. In Lightroom you can select from a small set of camera profiles - landscape, portrait, Adobe standard, etc.

Saving final edits as jpeg 12 is not visibly better than jpeg 8 or 9, but the files will be bigger. Presumeably 12 is offered in event you plan on editing them. However if you really want to preserve ALL the information and quality in your original capture and subsequent raw edits, you should be saving them as 16 bit Tiff or psd files in prophoto color space. If you choose to finish your images (raw converters are not intended for/lack the proper tools and capabilities to produce a truly "finished" image) - you are likely to get better results editing a 16 bit, uncompressed, wide gamut image compared with a high quality but compressed, standard gamut 8 bit jpeg.

So there are some changes made in raw converters which you have little control over, but if your goal is to preserve as much as possible jpeg is not a great choice.

f8lee Loc: New Mexico

First, the images you see on which you did no post processing were still in fact processed to a degree, in that a raw file (no capitalization required) is not an image at all, but rather is a stream of data from the imaging chip. It is is not an image at all until it is "de-mosaiced"

This makes sense once you understand how a digital sensor works.

Think of a digital imaging chip as a matrix of rows and columns, where an array of 6000 by 4000 would yield 24 million "dots" or pixels (picture elements). A raw file is the stream of data that comes from the sensor. With a few exceptions (Leica's monochrome, Foveon) ALL digital sensors, from that new Hasselblad to your smart phone camera, work as follows: while they too have a matrix of dots (called photo sites), each of those photo sites is covered with a colored filter that is either Red, Green or Blue. This is because the sensor chip itself is natively "color blind", each photo site can only register how many photons have struck it when exposed. The pattern of those colored filters (called the Bayer pattern) is R-G-G-B (for upper left, upper right,, lower left, lower right) - and there are twice as many green filters as there are red or blue because the human eye is more sensitive to green. Fuji's X-Trans chip uses a different pattern, but the concept is the same.

When an exposure is made, the data captured by the imaging chip is a bunch of values that represent how much light hit each photo site - and those measurements are all based on the light that made it through those filters. As a thought experiment, imagine a subject that was only pure blue - the photo sites with red and green filters above them would not register anything! Lots of black gaps in that file, eh?

So a raw file first needs to be rejiggered to become a true image file, where each image pixel has a stated RGB value. On the raw file, each spot has only an R OR a B OR a G value, but they are not blended. That process is called de-mosaicing, and the output of the process is the resultant image. Obviously there are a lot of calculations required to do this, but that's what the computer built into the camera (or phone) does. Cameras that only output JPEG do in fact create raw files to start with (there is no other option) but they quickly do the calculations and discard the raw file when the JPEG is created.

So, unlike a JPEG or TIF etc. file, the computer processing a raw file must interpret what actual color should appear at a given pixel, based on the readings made from the surrounding photo sites. There is no absolute lookup table, as there is for image file RGB values, to decide what color purple a given spot should be if one adjacent red reading was 500, another from the blue filter was 644 and yet another from a green filter spot was 42, or whatever. For those who say "yeah but you need a computer to interpret" any digital file!” I say that is actually incorrect - where a JPG specifies that RGB value (and leaves it to the hardware drivers and gear to not screw it up) the various demosaicing programs can actually result in different outputs from the same original raw file. Apple includes demosaicing software in OS X, but DxO, Phase One's Capture One, Adobe and others (including the camera manufacturers themselves) all have their own demosaicing software. While different software won't completely change the look of a given image, the subtle tonalities can well be different if you take an image and process it with C1 and compare that to the same raw file run through Adobe Lightroom.

By the bye, since you CANNOT see a raw image what you are looking at (on the back of the camera when you chimp, or on a computer screen) is a demosaiced image that has been interpreted by a computer, be it in the camera or on your desktop.

I hope that helps you understand how the system works.

Fotoartist Loc: Detroit, Michigan

I think you're process is sound. I like it. Shoot in Raw, process, then change to high quality JPEGs. Best of both worlds. Who wants to save 100mb files all the time? High quality JPEGs processed first in Raw are 99.8% as good.

f8lee Loc: New Mexico

You make a good point, but I discovered that old raw files are actually processed better with newer software. That is, 7+ years ago I had a Nikon D200 and processed the NEF files with DxO. Lately I've been culling my library of 50K images (spanning 17 years) and on a lark decided to reprocess some of those images using the latest version of DxO as well as LR - and the newly processed images were distinctively better. I guess as the demosaicing algorithms are improved you can bring new life to older images, so perhaps it's worth keeping the original raw files after all.

burkphoto Loc: High Point, NC

This is absolutely true. A raw file is just digitized photoreceptor data. It has to be developed and processed into an image. That requires keeping some of the data and discarding the rest. However, the original raw file is *never* changed. You can save a TIFF, PSD, JPEG, etc., but that is just a processed copy.

So... If you get a new post-processing program with advanced algorithms, you may get much better results from an old raw file, more easily, than you did 10-15 years ago. Of course, you've probably learned a lot since then, too!

f8lee Loc: New Mexico

And thus the moral of the story is it's worth keeping those raw files!

robertjsmith

I would like to thank all of you for the very good description of the process. I wasn't clear at the process but all of you have helped me very much. So again thank all of you!

Bob

Steve Perry Loc: Sylvania, Ohio

Excellent explanation!

bpulv Loc: Buena Park, CA

Hi Art,

First of all, RAW data is not "processed" in the camera. The picture data in a NEF file is the unaltered stream of binary "1's" and "0's" that the camera recorded. The NEF file also contains additional data such as the metadata, but the RAW picture data is the exact stream of data that was generated by your camera's sensor.

JPG files by definition are compressed files. The process of compressing a file both combines and discards raw data using an algorithm that is unique to the camera or computer program that is used to make the conversion. It is not unexpected that the JPG files made by the camera would be different from the JPG files converted in an editing program since they use two different algorithms to generate the JPG file.

robertjsmith

O.K. you guys, your helping me very much so lets discuss converting to another format such as PNG or TIFF?
Bob